Low profile patient specific cutting blocks for a knee joint

ABSTRACT

A low profile patient specific cutting block for a knee comprises a plurality of bone interfacing portions and a cutting slot. The plurality of bone interfacing portions are configured to overlie portions of an end of a bone. The bone interfacing portions each have a surface generally a negative of the portion of the bone the bone interfacing portion overlies. The bone interfacing portions are angularly offset from each other such that a first of the bone interfacing portions overlies an anterior portion of the bone and a second of the bone interfacing portions overlies a portion of bone generally perpendicular to the anterior portion of bone. The cutting slot is oriented in a fixed position relative to the bone interfacing portions such that the cutting slot directs a cutting tool at a fixed angle and at a fixed depth from the bone interfacing portions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/033,419, filed Mar. 3, 2008 and further claims the benefit of U.S.Provisional Application No. 61/089,373, filed Aug. 15, 2008. Thedisclosure of each application is incorporated by reference in itsentirety.

FIELD OF THE INVENTION

This invention relates generally to cutting blocks for bone resectionsat a knee joint and, more particularly, for cutting blocks designed fora patient's specific bone and cartilage and further configured to asurgeon's preferences.

SUMMARY OF THE INVENTION

It is in view of problems related to the field above that the presentinvention was developed.

In one aspect of the invention, a low profile patient specific cuttingblock for a knee comprises a plurality of bone interfacing portions anda cutting slot. The plurality of bone interfacing portions areconfigured to overlie portions of an end of a bone. The bone interfacingportions each have a surface generally a negative of the portion of thebone the bone interfacing portion overlies. The bone interfacingportions are angularly offset from each other such that a first of thebone interfacing portions overlies an anterior portion of the bone and asecond of the bone interfacing portions overlies a portion of bonegenerally perpendicular to the anterior portion of bone. The cuttingslot is oriented in a fixed position relative to the bone interfacingportions such that the cutting slot directs a cutting tool at a fixedangle and at a fixed depth from the bone interfacing portions.

In another embodiment of the invention the low profile patient specificcutting block is a femoral cutting block. The block further comprisesbosses having a thickness and an aperture extending through the bosses.The aperture has a diameter. The bosses are configured to direct a pinthrough the boss. The thickness of the boss is greater than the diameterof the aperture.

In yet another embodiment, the bone interfacing portions are generallyoriented in the middle of the low profile patient specific cutting blockin an anterior portion of the low profile patient specific cutting blockand are oriented medially and laterally at a posterior portion of thelow profile patient specific cutting block.

Alternatively, the low profile patient specific cutting block is atibial block and the cutting slot is offset and medialized relative tothe tibial bone.

Another embodiment includes a paddle extending posteriolaterally from amiddle portion of the patient specific cutting block. The paddle has araised portion anteriorly oriented on the low profile patient specificcutting block such that the paddle does not touch the tibia on ananterior proximal surface and does touch the tibia on a posteriorproximal surface.

Further features, aspects, and advantages of the present invention, aswell as the structure and operation of various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate embodiments of the present invention andtogether with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a view of a knee joint with a femoral patient specific cuttingblock and a tibial patient specific block;

FIG. 2 is an anterior view of a femoral patient specific cutting blockaccording to an aspect of the invention;

FIG. 3 is a proximal posterior view of a femoral patient cuttingspecific block according to an aspect of the invention;

FIG. 4 is an anterior view of a tibial patient specific cutting blockaccording to an aspect of the invention; and

FIG. 5 is a distal posterior view of a tibial patient specific cuttingblock according to an aspect of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to the accompanying drawings in which like reference numbersindicate like elements, FIG. 1 illustrates a view of a knee joint with afemoral patient specific cutting block 10 and a tibial patient specificblock 14. The femoral patient specific cutting block 10 is attached to afemur 12. The tibial patient specific cutting block 14 is attached to atibia 16. The patient specific cutting blocks 10 and 14 are configuredto engage portions of bone and cartilage on the femur 12 and tibia 16 toalign cutting surfaces within the patient specific cutting blocks sothat a distal cut (on the femur) and a proximal cut (on the tibia) maybe made without using either intramedullary or extramedullary guides.

The femoral patient specific cutting block 10 includes an anteriorfemoral portion 20, a medial femoral paddle 22 and a lateral femoralpaddle 24. These portions overlie portions of the anterior face, medialcondyle and lateral condyle of the femur 12, respectively. Because theportions 20, 22, and 24 only overlie portions of the femur 12 instead ofan entire conforming overlay of the end of the femur 12, the patientspecific cutting block 10 may have a lower profile, both in themedio-lateral and anterior-posterior direction.

Pin holes 40 and 48, guide bosses 42, a mechanical axis index 44, and afemoral cutting slot 46 are oriented on the exterior surface of thefemoral patient specific cutting block 10. The pin holes 40 and 48 areoriented to pin the cutting block 10 to the femur 12. Guide bosses 42are oriented in order to set pins for the other box cuts necessary toprepare the femur 12 for an implant.

The pin holes 40 and 48 are oriented on the anterior face of the patientspecific cutting block 10. The pin holes 40 and 48 may have bosses (asshown with reference to pin holes 40) or may be flush with the surface(as shown with pin hole 48). The bosses may be used to direct the pins,for example, away from the edges of the bone. The low profile of thepatient specific cutting block 10 would allow a pin hole without a bossto allow a pin to extend in a wide variety of angular directions. Byextending bosses a thickness greater than the diameter of the aperturethrough the boss, the bosses may orient the pins by adding a guidethrough the patient specific cutting block 10 so that the pins aredirected as they are impacted or drilled into the bone.

The mechanical axis index 44 is oriented along the mechanical axis ofthe femur 12. A cutting slot 46, oriented relative to anatomicalstructures and defined by the surgeon, directs the distal cut for animplant. As will be described below, MR and X-rays of the patient areused to align the mechanical axis index 44 to the patient specificcutting block 10.

In addition to the MR and X-ray information, surgeon preferences areused to place the cutting slot 46 on the patient specific cutting block10. The cutting slot 46 may be oriented relative to the mechanical axisin a varus or valgus orientation (according to surgeon preference basedupon the X-ray data). The flexion gap may be adjusted by adjusting theangle of the cutting slot 46 relative to the patient specific cuttingblock 10. The depth of the resection cut is also determined by theplacement of the cutting slot 46 and is determined from the distal pointon the condyles.

The guide bosses 42 are also placed on the patient specific cuttingblock 10 according to MR data, X-ray data and surgeon preference. Theguide bosses 42 may set the rotation of the implant by adjusting theposterior bosses 42 relative to one another. The relative placement ofthe bosses 42 allows for pins to be placed so that the pins guide afurther cutting guide over the distal cut of the femur in order to makethe anterior and posterior cuts and any chamfer cuts required by thebone interfacing surfaces of the implant. Internal/external rotation isdirected by moving the depth of one of the posterior bosses relative tothe other posterior boss. A-P placement of the implant is adjusted bymoving both of the posterior bosses 42 together in the A-P direction.

The tibial patient specific cutting block 14 includes an anteriorfemoral portion 300, a medial femoral paddle 32 and a lateral femoralpaddle 34. These portions overlie portions of the anterior face, medialplateau and lateral plateau of the tibia 16, respectively. Because theportions 20, 22, and 24 only overlie portions of the tibia 16 instead ofan entire conforming overlay of the end of the tibia 16, the patientspecific cutting block 14 may have a lower profile, both in themedio-lateral and anterior-posterior direction.

Pin holes 50 and 52, an M-L index 54 and a cutting slot 56 are orientedon the outer surface of the tibial patient specific cutting block 14.The pin holes 50 and 52 may fix the patient specific cutting block 14 tothe bone and may additionally align the pins relative to one another forfurther orientation, if necessary, in tibial preparation.

The tibial cutting slot 56 is medialized relative to the anteriorsurface of the tibia 16 (i.e., the tibial cutting slot 56 is oriented onthe medial half of the anterior side of the patient specific cuttingblock 14). The lateral paddle 34 may extend around the front of thetibial eminence extending posterior-laterally toward the lateralplateau. These features may allow the guide to be used in a MISprocedure, where lateral clearance is minimized by cutting the tibiafrom the medial half of the anterior face of the tibia while minimizingthe medial approach to the tibia, which would involve additional softtissue issues. Thus, the medialized and rotated cutting slot 56 isoriented for clearance and accessibility even for an MIS approach.

Turing now to FIGS. 2 and 3. FIG. 2 is an anterior view of a femoralpatient specific cutting block according to an aspect of the invention.FIG. 3 is a proximal posterior view of a femoral patient cuttingspecific block according to an aspect of the invention. In addition tothe features described above, the patient specific cutting block 10 mayalso include an epicondylar index 68. The epicondylar index 68 may beused as a visual “feel good” for the rotation of the holes and the A-Pplacement of the holes, similar to the purpose of the mechanical axisindex described above.

In FIG. 3, the bone interfacing surfaces 80, 82, 84 and 86 are shown.The anterior bone interfacing portion overlies a portion of the anteriorsurface of cartilage and bone. The medial bone interfacing portion 82,the lateral bone interfacing portion 84 and the intracondylar boneinterfacing portion 86 overlie the medial, lateral and intracondylarnotch portions of the condyles, respectively. The bone interfacingportions 80, 82 and 84 align to the anterior and distal faces of thefemur while the intracondylar bone interfacing portion 86 orients theblock medio-laterally. By using relatively small portions of thesurfaces, the profile of the patient specific cutting block 10 may belowered. Additionally, the fit may be better as smaller portions mayresult in fewer osteotomes on the bone surface (which may cause poor fitof the patient specific cutting block to the bone. The paddles 22 and 24may also be relatively thin posteriorly. This further minimizes theprofile of the patient specific cutting block.

The cutting slot 46 may be formed through the bone interfacing portionsof the patient specific cutting block or may be recessed from thesurface. The thickness of the cutting slot helps to direct theorientation of the cutting tool as the cutting tool advances through thecutting slot 46. As previously discussed, the relative angle of thecutting slot 46 to the patient specific cutting block 10 (andparticularly to the bone interfacing portions) orients the flexion gapwhile the translation of the cutting slot 46 relative to the patientspecific cutting block 10 sets the resection depth.

Turing now to FIGS. 4 and 5, FIG. 4 is an anterior view of a tibialpatient specific cutting block according to an aspect of the invention.FIG. 5 is a distal posterior view of a tibial patient specific cuttingblock according to an aspect of the invention. In addition to thefeatures described above, the tibial patient specific cutting block alsomay include a posterior chamfer 96 and a planar proximal surface 100.The posterior chamfer 96 allows for the tibial patient specific cuttingblock to be positioned posteriorly without distracting the soft tissuearound the knee more than necessary. Similar to other features, thisfeature helps the overall profile of the implant.

The planar proximal surface 100 may match the distal femur resectionplane from the femoral patient specific cutting block. This feature mayallow intraoperative flexion/extension testing when the tibial patientspecific cutting block is secured to the tibia.

Bone interfacing surfaces 90, 92, and 94 are shown in FIG. 5. Theanterior bone interfacing portion 90 overlies a portion of the anteriorsurface of cartilage and bone. The medial bone interfacing portion 92and the lateral bone interfacing portion 84 overlie the medial andlateral portions of the tibia, respectively. The bone interfacingportions 92 and 94 align to the proximal faces of the tibial plateaus(thus orienting the patient specific cutting block proximally) while theanterior bone interfacing portion 90 orients the block medio-laterallyand in the AP direction. By using relatively small portions of thesurfaces, the profile of the patient specific cutting block may belowered. Additionally, the fit may be better as smaller portions mayresult in fewer osteotomes on the bone surface (which may cause poor fitof the patient specific cutting block to the bone. The paddles 32 and 34may also be relatively thin posteriorly and may be elevated from thetibial plateau surface anteriorly to avoid poor placement. This furtherminimizes the profile of the patient specific cutting block.

The cutting slot 56 may be formed through the bone interfacing portionsof the patient specific cutting block or may be recessed from thesurface. If the cutting slot 56 is recessed from the surface, thenimpingement of the block on bone may be minimized, again increasing thefit of the patient specific cutting block to the bone. The thickness ofthe cutting slot helps to direct the orientation of the cutting tool asthe cutting tool advances through the cutting slot 56. As previouslydiscussed, the relative angle of the cutting slot 56 to the patientspecific cutting block 10 (and particularly to the bone interfacingportions) orients the flexion gap while the translation of the cuttingslot 46 relative to the patient specific cutting block 10 sets theresection depth.

The MR data and X-ray data may be taken by known means. As an example,the following protocols may be used. Different MR protocols may beexecuted on different patients. To minimize scan time, a fast spin echoimaging technique may be used for any protocol, essentially producing aproton density (PD) weighted image. One protocol may use the spoiledgradient echo technique with a low repetition time (TR) and low echotime (TE) and a flip angle of 30 degrees combined with a fat saturationtechnique. A second protocol and third protocol may use a high TR and alow TE combined with a fat saturation technique. The only differencebetween the second protocol and third protocol is that the secondprotocol has lower TE than the third protocol, which in turn offers moreT1 and less PD properties. The increased T1 relaxation time may help toincrease the image contrast within the different tissues in the MRimage.

Bone models of the femur and tibia may be extracted from the MR imagesand appropriate anatomic reference landmarks may be identified. Full legx-rays may be used to determine the mechanical axis alignment. Femoraland tibial cutting blocks may then be designed through computer aideddesign (CAD) modeling such that they conform to the bone models on oneside for proper seating and have cutting slots at the appropriateresection depth and angle specific to the patient. The cutting blocksmay be made from medical grade Nylon 12 using the EOSint P system. Sincethe surface geometries of these blocks are based on the patient's MRdata set, clean data (properly differentiating between bone andcartilage and soft tissue) should be used to ensure the fit andfunctionality of the blocks.

In view of the foregoing, it will be seen that the several advantages ofthe invention are achieved and attained.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims appended hereto and their equivalents.

1-5. (canceled)
 6. A low profile patient specific cutting block for aknee, comprising: a plurality of bone interfacing portions configured tooverlie portions of an end of a bone, the bone interfacing portionsangularly offset from each other, a cutting slot oriented in a fixedposition relative to the bone interfacing portions to direct a cuttingtool at a fixed angle relative to the bone interfacing portions; and ananteriorly-facing exterior surface defining an index marking extendingin a superior-inferior direction transverse to a longitudinal axis ofthe cutting slot to provide an indication of the orientation of thepatient specific cutting block relative to the bone.
 7. The low profilepatient specific cutting block of claim 6, wherein the index markingcomprises an M-L index axis positioned between a medial portion and alateral portion of the patient specific cutting block.
 8. The lowprofile patient specific cutting block of claim 6, wherein the indexmarking comprises a mechanical index axis positioned between a medialportion and a lateral portion of the patient specific cutting block, themechanical index axis being generally aligned with a mechanical axis ofthe bone to provide the indication of the orientation of the patientspecific cutting block relative to the bone.
 9. The low profile patientspecific cutting block of claim 6, wherein the index marking comprises agroove or score extending into the anteriorly-facing exterior surface ofthe patient specific cutting block.
 10. The low profile patient specificcutting block of claim 6, wherein the index marking is positioned alonga mid-portion of the patient specific cutting block between a medialportion and a lateral portion of the patient specific cutting block. 11.The low profile patient specific cutting block of claim 6, wherein afirst of the bone interfacing portions extends in a first direction anda second of the bone interfacing portions extends in a second directiongenerally perpendicular to the first direction.
 12. The low profilepatient specific cutting block of claim 6, wherein the bone interfacingportions each have a surface that is generally a negative of the portionof the bone that the bone interfacing portion is configured to overlie,wherein a first of the bone interfacing portions is configured tooverlie an anterior portion of the bone extending in a first direction,and wherein a second of the bone interfacing portions is configured tooverlie another portion of the bone extending in a second directiongenerally perpendicular to the first direction.
 13. The low profilepatient specific cutting block of claim 12, wherein the first of thebone interfacing portions is configured to overlie an anterior face ofthe bone, and wherein the second of the bone interfacing portionsincludes a first portion configured to overlie a medial portion of thebone and a second portion configured to overlie a lateral portion of thebone.
 14. The low profile patient specific cutting block of claim 6,wherein the patient specific cutting block further comprises a pluralityof bosses each having a thickness and an aperture extendingtherethrough, the aperture having a diameter sized and configured todirect a pin therethrough, the thickness of the boss being greater thanthe diameter of the aperture.
 15. The low profile patient specificcutting block of claim 6, wherein the bone interfacing portions furtherinclude medial and lateral paddles positioned medially and laterally ata posterior portion of the patient specific cutting block, and whereinthe medial and lateral paddles each have a raised portion anteriorlyoriented on the patient specific cutting block such that the paddles donot touch the tibia on an anterior proximal surface and do touch thetibia on a posterior proximal surface.
 16. The low profile patientspecific cutting block of claim 6, wherein the bone interfacing portionsinclude an anterior portion generally positioned along the mid-portionof the patient specific cutting block, and wherein the bone interfacingportions further include medial and lateral paddles positioned mediallyand laterally at a posterior portion of the patient specific cuttingblock, and wherein the index marking extends along the anterior portionof the patient specific cutting block.
 17. The low profile patientspecific cutting block of claim 6, wherein the patient specific cuttingblock is a tibial cutting block and the cutting slot is medially offsetrelative to an anterior portion of the bone and is oriented entirelyalong a medial half of the tibial cutting block and does not extendalong a lateral half of the tibial cutting block; and wherein thecutting slot opens at a lateral opening defined by the tibial cuttingblock, the lateral opening facing the lateral half of the tibial cuttingblock.
 18. The low profile patient specific cutting block of claim 6,further comprising an epicondylar index marking extending in amedial-lateral direction to provide an indication of a rotationalposition of the patient specific cutting block relative to the bone. 19.The low profile patient specific cutting block of claim 18, wherein thepatient specific cutting block is a femoral cutting block, and whereinthe epicondylar index marking comprises a groove or score extending intothe anteriorly-facing exterior surface of the femoral cutting block. 20.A low profile patient specific cutting block for a knee, comprising: aplurality of bone interfacing portions configured to overlie portions ofan end of a bone, the bone interfacing portions angularly offset fromeach other; a cutting slot oriented in a fixed position relative to thebone interfacing portions to direct a cutting tool at a fixed anglerelative to the bone interfacing portions; and wherein the patientspecific cutting block comprises a tibial cutting block, and wherein thecutting slot is medially offset relative to an anterior portion of thebone and is oriented entirely along a medial half of the tibial cuttingblock and does not extend along a lateral half of the tibial cuttingblock.
 21. The low profile patient specific cutting block of claim 20,wherein the cutting slot opens at a lateral opening defined by thetibial cutting block, the lateral opening facing the lateral half of thetibial cutting block.
 22. The low profile patient specific cutting blockof claim 20, wherein a first of the bone interfacing portions extends ina first direction and a second of the bone interfacing portions extendsin a second direction generally perpendicular to the first direction.23. The low profile patient specific cutting block of claim 20, whereinthe bone interfacing portions each have a surface that is generally anegative of the portion of the bone that the bone interfacing portion isconfigured to overlie, and wherein a first of the bone interfacingportions extends in a first direction and a second of the boneinterfacing portions extends in a second direction generallyperpendicular to the first direction.
 24. The low profile patientspecific cutting block of claim 20, wherein the patient specific cuttingblock includes an anteriorly-facing exterior surface defining an indexmarking extending in a superior-inferior direction transverse to alongitudinal axis of the cutting slot to provide an indication of theorientation of the patient specific cutting block relative to the bone.25. The low profile patient specific cutting block of claim 24, whereinthe index marking comprises a mechanical index axis positioned along amid-portion of the patient specific cutting block between a medialportion and a lateral portion of the patient specific cutting block, themechanical index axis being generally aligned with a mechanical axis ofthe bone to provide the indication of the orientation of the patientspecific cutting block relative to the bone.